Methods, compositions and blends for forming articles having improved environmental stress crack resistance

ABSTRACT

Several processes for the manufacture of thin-walled tubes are described, including: injection molding an article and annealing the article, injection molding a blend of a polymer and a high melt flow polymer, injection molding a blend of a polymer and nanoparticles or nanocomposites. Using nanoparticles to improve ESCR and/or tear resistance of a polymer or blend is also disclosed.

FIELD OF THE INVENTION

The present invention according to one aspect, relates to a process forthe manufacture of flexible thin-walled articles, such as tubes or thelike, wherein an improvement in Environmental Stress Crack Resistance(ESCR) and other properties is provided by annealing of the articleafter forming to its final shape. There are also provided, according tofurther aspects of the invention, compositions and blends that may beuseful in the manufacture of flexible thin-walled articles or otherarticles, the compositions and blends having improved ESCR and otherproperties.

DISCUSSION OF THE PRIOR ART

Thin-walled tubular containers, such as those used in the cosmeticsindustry, are currently produced mainly by a combination of extrusionand cutting-to-length of the tube body, injection moulding of the headand shoulders and the welding of the body to the head and shoulders. LowMelt Flow Index (MFI) polyethylene (MFI generally less than 2) is thepreferred polymer for tube manufacture as it generally imparts theproperties of good “feel” and flexibility required by customers and issuitable for extrusion processing. In addition, low MFI low densitypolyethylene (LDPE) offers sufficient product resistance and barrierproperties to make it suitable for most products currently packed intotubes. In cases where the barrier properties of polyethylene areinadequate for particular applications, medium density polyethylene(MDPE), high density polyethylene (HDPE), polypropylene (PP) andmultilayer polymer films are commonly used. Because the body of the tubeis extruded, low MFI polymers with inherently good ESCR are able to beused in their manufacture. In addition, being a relatively low shearrate process, the extrusion process introduces minimal stresses andmolecular orientation of the polymer into the tube body duringmanufacture. The use of polymers with inherently good ESCR, the relativelack of molecular orientation in extruded and extrusion/blow-mouldedtubes as well as the relatively low pressures and processing speedsinherent in the extrusion process results in extruded tubes having lowbuilt-in stresses and inherently good ESCR. Consequently, stress reliefof extruded tubes by annealing is of minimal value for the vast majorityof applications and tube types.

While the injection moulding of flexible thin walled articles such astubes has been proposed, prior to the developments described inPCT/AU98/00255 (the '255 patent), which is incorporated herein byreference, it has not been possible to injection mould such articleshaving relatively long, thin sections without the articles being toosusceptible to failure to be of commercial or practical use. The mainproblems have been associated with the polymers used to injection mouldtubes, in that the process of injection moulding a cylindrical or othershaped tube requires the polymer to simultaneously have a high MFI toenable the polymer to flow down the long, narrow and curved pathdictated by the tube shape without the use of excessive injectionpressures, yet to have sufficiently good mechanical properties to beable to withstand handling and resist the stress cracking effects ofmany of the products that will be packed in it. To infection mould atube requires the polymer/polymer blend to have flow properties capableof forming moulded parts with radii and a length/thickness ratio of 100and often much higher, such as over 350. Typically the polymer orpolymer blends are required to have an MFI of greater than 10,preferably greater than 20, more preferably greater 30 and frequentlygreater than 50. It is well known that the physical properties ofpolymers, particularly ESCR, decrease significantly as the MFIincreases, so the inherent ESCR properties of polymer/polymer blendswith MFIs required for injection moulded tubes are significantly andinherently lower than those for extruded tubes. To compound thisproblem, forcing a polymer to flow in a mould with such dimensionsintroduces severe stresses into the polymer, these stresses being“frozen” into the article thus produced when the polymer rapidly coolsbelow its crystallising temperature before these stresses can berelieved. These stresses result in the tube having surprisinglydifferent and deteriorated properties relative to the other productsmoulded from the same polymers under less severe moulding conditions.

Further stresses are introduced into injection moulded tubes when theyare filled with product and then crimped and sealed—most often by heatsealing or ultrasonic welding. This process often involves bending the‘open’ end of the tube back on itself through an angle of up to 180° toform a fold at the edge of the seal. This fold is in the direction ofthe flow of the polymer during moulding, which direction having beendemonstrated to be the direction of maximum weakness of the mouldedproduct. This ‘folded and sealed’ area, where the tube is required to bedeformed in order to effect a seal, is an area of the injection-mouldedtube particularly susceptible to stress and flex cracking. Similarly,the body of the tube is permanently distorted, and consequentlyadditionally and permanently stressed, by the crimping/sealing process,as can be readily seen from the distorted shape of the crimped andsealed tube relative to its uncrimped and unsealed shape. Thesestresses, especially those induced by permanent distortion of thearticle after crimping and sealing, but also those imposed during thesqueezing and flexing of the tube during use, have the effect ofsignificantly reducing the ESCR and other physical properties of thepolymers make up the injection moulded article, thereby make itnecessary to use polymers that display unusually good ESCR and otherphysical properties when moulded into that desired articles. Suchpolymers/blends may have a number of disadvantages relative to otherpolymers/blends, such as being more expensive, requiring longer coolingtimes (and hence longer cycle times), having higher stiffness (ie.poorer ‘feel’), requiring more intense or expensive compounding, etc.

The following examples illustrate the exceptionally high level ofstresses that are moulded into tubes when they are manufactured usingthe injection moulded process as opposed to the extrusion process.

Tubes with 120×35 mm dimensions were injection moulded using DuPont2020T polymer, a 1.1 MFI polymer extensively used in commercial extrudedtube manufacture and which DuPont describes as “especially suited forinjection moulded closure and extruded tubing where flexibility andmaximum resistance to environmental stress cracking is required”. Theinjection-moulded tubes were moulded with extreme difficulty, requiringvery high injection pressures and temperatures simply to get the 2020Tto fill the mould. In each moulding significant degrees of coreshifting/flexing were noted, due no doubt to the extremely highinjection pressures that were required. In addition, it was noted thatthe tubes had visually no resistance to flexing in the direction of thematerial flow, with significant cracking being induced with loss than 5manual squeezes of the tube. The environmental stress cracking of thesame tubes was tested using the ESCR test as herein described a in spiteof claims of “maximum resistance” to environmental stress cracking, wasfound to be totally in adequate for moulding thin-walled tubes byinjection moulding. This is in stark contrast with its status as a‘polymer of choice’ for tubes made by the extrusion process. Thedramatic degradation of the properties of 2020T when injection mouldedis almost exclusively due to the exceptionally high level of moulded-inand oriented stresses relative to those in tubes extruded from the samematerial.

In another illustration of the very high level of moulded-in stressesinherent in injection moulded tubes, Dowlex 2517, a 25 MFI LLDPEs wasmoulded into 150×50 mm tubes. In a pamphlet on its Dowlex LLDPEs. Dowadvises that LLDPEs have substantially better ESCR properties thanequivalent high pressure LDPE. To illustrate the difference, a Dowpamphlet states that in one comparative test a high flow Dowlex LLDPEhas an ESCR in oil some 80 times better than that achieved by a highpressure LDPE with the similar density and MFI (5700 hrs, compared to 70hrs). It states that the LLDPE has an ESCR approximately 10 times betterthan the LDPE when immersed in a 10% Teric solution at 50° C. (225 hrscompared to 26 hrs). However, contrary to these observations, we havefound that when these polymers are moulded in the form of thin walledtubes and ESCR subsequently tested using the ESCR test as hereindescribed both Dow's ‘Dowlex’ LLDPE 2517 and Kemacor's LD 8153 (a highpressure LDPE with similar MFI and density) performed poorly in 10%Teric N9 at 50° C., and both failed within 20 minutes, an ESCR that isof the order of 600 times less d=that indicated in the pamphlet. Theextreme degradation in the ESCR performance of both polymers wheninjection moulded into tubes is almost exclusively the result of thehigh level of moulded-in and oriented stresses in the injection mouldedtubes.

As an indication of the extent of the increase in Strain in the area ofa tube that is folded and sealed relative to the unsealed (i.e. open)tube, the stain on the area resulting from scaling was calculated usingthe formula:Strain in polymer=Radius of fold/Square of the thickness of the strip.

Assuming a nominal radius for a flat polymer strip of 1 metre and astrip thickness of 0.5 mm (a typical wall thickness for a tube), thestrain on the unsealed polymer is 0.00025. When sealed, the radius ofthe strip at the edge of the seal is of the order of 0.65 mm, resultingin a calculated strain of 0.385. In other words, sealing the tuberesults in an increase in strain in the polymer of over 1600 times thatin an unsealed tube. For extruded tubes, with their inherently higherESCR polymer and significantly lower moulded-in processing stresses,this increase in strain presents few problems in terms of ESCR and/ortear strength performance. That is, annealing articles made using thesepolymers in combination with the extrusion process is not like to resultin noticeable and/or commercially valuable improvements in ESCR and tearstrength of the article. However, the applicant has found that when insection moulding thin wall flexible articles, with their significantlyhigher moulded-in and oriented stresses and being formed fromintrinsically lower ESCR polymers and hence having greater inherentsusceptibility to flex and ESCR failure, annealing can make asignificant difference to both the ESCR and/or tar strength of thearticle. Such improvements may mean the difference between functionalityand non-functionality of the article in terms of its commercialapplication.

We have now found that annealing flexible injection moulded thin walledarticle just before, during or after the article has been fined and/ordistorted to its final required shape significantly improves the ESCRand a number of other physical properties of the article, such asresistance to tearing in the direction of the polymer flow when measuredusing the Gullwing Tear test method (ASTM D-1004). These improvementsare most noticeable in the areas of the article that have had additionalstresses imposed on them such as occur as a result of any distortion ofthe article during and subsequent to sealing or having load imposed onit by, for example, stacking. An additional benefit of the annealing ofthe present invention is that increasing their ESCR etc. enables the useof polymers/blends for the manufacture of flexible thin-walled articlesthat would, in their unannealed condition, result in flexible thinwalled articles that are either marginal or unsuitable for packagingparticular products. During the annealing process the article may, ifheated or otherwise treated sufficiently to soften, and/or in caseswhere the article is sufficiently supported to prevent unwanteddistortion of the article, melt the polymer, be reshaped by theapplication of appropriate forces by various equipment.

While not wishing to be bound by the proposed theory, it is believedthat the rapid cooling of the polymer during the injection moulding stepfrom a molten state to below the solidification temperature of thepolymer results in various stresses and being captured in the solidpiece, and that filer stresses are introduced as a result of thedistortion of the article resetting from the sealing process. Thesestresses make the article more susceptible to attack by stress crackagents and physical flexing, and hence to failure. This is particularlythe case in the period immediately after filling and sealing when, dueto the distortion of the moulding resulting from sealing, the stresseswith the moulding are at their highest (to an extent, they ‘relax’ anddissipate over an extended time) and the stress crack agent is in directcontact with the article and can ‘attack’ the highly stressed areas inthe period subsequent to filling and scaling to cause failure. It isbelieved that by annealing the polymer the stresses are relieved beforethe stress crack agents are able to ‘attack’ the stressed polymer inorder to cause failure. If the stresses are not immediately relieved, itis believed that for many polymer formulations the stress crack agent isable to cause failure of the article before the ‘normal’ relaxation ofthe polymer is able to reduce the susceptibility to article failure.

The degree of moulded-in stresses, and hence the degree of reduction inESCR and other proper performance can vary somewhat from moulding tomoulding and over time. Thus it is difficult to reliably and accuratelycompensate for the variation in ESCR reduction between mouldings in theabsence of annealing treatment. A further complication is that due tothe dual reduction in stresses over time together with the fact that theextent of stress reduction will depend on the conditions (primarily timeand temperature) under which the articles are stored prior to and afterfilling and sealing, it is not possible to reliably and consistentlyforecast how long it may take for all tubes made from a particularpolymer formulation to become suitable for use due to natural stressreduction. For this reason amongst others, in order to minimise thepossibility of commercial failure due to inadequate ESCR and otherproperty performance, it is currently generally necessary to usepolymers with proven exceptionally good ESCR performance when in astressed state. This requirement has a number of potentially negativeaspects, in particular in the areas of potentially higher polymer/unitcost increased cycle times and less-than-ideal ‘feel’ and flexibility.It is therefore advantageous if the moulded-in stresses can be relievedbefore they can substantially adversely affect the commercialperformance of the thin walled article.

It has been found that, provided the moulded-in stresses in theinjection moulded article are relieved to a greater or lesser extentbefore the stress crack potential of the product that is filled into thearticle sufficient time in contact with the polymer in its stressedstate to cause or initiate cracking, flexible thin walled injectionmoulded articles with improved ESCR and other property performance canbe produced. Further, it has been found that annealing articles enablesa much wider range of polymers and polymer blends to be used in themanufacture of commercially useful flexible thin walled articles than isthe case if annealing is not practiced.

If there is a significant time lapse the moulding and filling & sealingoperations (e.g. if the article is moulded in one location, packed andthen shipped to another location for filling and sealing) and it isdesired to effect annealing of the moulding prior to the article beingshipped—most conveniently, immediately post moulding—many of thebenefits of annealing just prior to, during and/or after distortion ofthe article can still be achieved by annealing post moulding. Thebenefits of this way not as produced as those that can be achieved byannealing after the article has been distorted but may, depending on thepolymer formulation and moulding conditions, nevertheless be worthwhile.

The benefits of annealing post moulding but pre filling are mostnoticeable in areas of the moulding that are subjected to leastadditional stresses upon crimping and scaling. These areas are mostfrequently those that are relatively distant to the ‘crimp and seal’area—for example, those areas relatively near the head and shoulders ofa tube. We have found that areas of the moulding that are annealed,allowed to cool (if the annealing process elevates the temperature ofthe moulding above its preannealing temperature) and then subjected toconsiderable distortion such as occurs in and around the sealed area ofthe tube during a crimp and seal operation may manifest dramaticallydeteriorated ESCR performance relative to the same considerablydistorted areas in equivalent unannealed mouldings. This is illustratedby the ESCR test as herein described, in which three sets of strips ofthe polymer blend taken from the same area of the mouldings weresubjected to said ESCR test. One set of strips was annealed afterbending and stapling, another set was not annealed and the third set ofstrips was annealed prior to bonding and stapling. The ESCR results wereas follows:

-   -   Only 4% of strips annealed after bending and stapling failed        within 190 hrs    -   25% of the unannealed strips failed within 190 hrs    -   Virtually all (94%) of strips annealed before banding and        stapling failed within only 3.5 hrs.

DESCRIPTION OF THE INVENTION

As the above results illustrate, annealing tubes when they are in astressed state significantly improves their ESCR relative to unannealedtubes, whereas annealing tubes in an unstressed state and subsequentlystressing them results in dramatically reduced ESCR.

Thus, according to a first aspect of the present invention there isprovided a process for the manufacture of flexible thin-walled articlescomprising injection moulding a body of the article from a plasticsmaterial; adapting the body to form a base of the article; and annealingthe plastics material.

Annealing is generally defined as the process for removing ordiminishing the strains and stresses in therapeutics. It is oftenachieved by heating the substance to be annealed and then allowing it togradually cool. Two successful techniques often employed when annealingthermoplastics include one which withdraws the thermoplastics from aheat source, and the other which causes the heat from the heat source todiminish. Both techniques are often referred to as bulk annealingtechniques since they involve heating the interior and exterior of thethermoplastics. The former is generally achieved in lehrs and the latteris generally achieved in ovens. Additional techniques for bulk annealingthermoplastics include those which employ infrared radiation. Thermalannealing is often the preferred method of annealing since simpleequipment and techniques are widely and inexpensively available topractice the step. In other, less preferred embodiments, the annealingcan be practiced by applying pressure, expression, or tension for ashort time.

It is of increasing interest to reduce the stresses and strains ofthermoplastics without employing bulk annealing techniques such as theabove-described. Accordingly, a process for reducing strains inthermoplastics by surface annealing may be employed which unexpectedlyand simultaneously preserves the physical and chemical properties of thethermoplastics. Surface annealing is defined as heating the outer layerof the thermoplastic which is the external layer of the thermoplasticthat often no more than half the thickness of the area to be annealed,for example, 0.25 mm thick in the case of a 0.5 mm wall-thicknessarticle. Moreover, there is no initiation with respect to the heatsource being utilized in this surface annealing other than that it doesnot cause the outer layer of the thermoplastic and the internal portionof the thermoplastic to be heated to the same temperature, wherein theinternal portion is defined as any part of the thermoplastic notincluding the outer layer as previously defined. Thus heat may penetrateinternal portion; however, the internal portion is cooler defined theouter layer after the outer film layer is surface annealed. Therefore,bulk annealing is prevented. Surface annealing is particularly effectivein terms of increasing the ESCR of a thin walled flexible article whenthe surface that is annealed is the surface that will come into contactwith the stress crack agent. The interior wall of a tube or othercontainer, in preference to the exterior wall of a tube or othercontainer, is an example of a surface for which surface annealing isparticularly effective. This is because an annealed interior wall of atub or other container presents the stress crack agent with a surfacewith reduced stress and hence an improved ESCR relative to an unannealedinterior wall, thereby minimising the chances of the stress cock agentbeing able to initiate stress cracking that could eventually lead to thefailure of the tube or container. If the outer surface of the tube orcontainer is the annealed surface, the stress crack agent is able toinitiate cracking in the unannealed interior surface with which it is inimmediate contact, thereby potentially weakening the tube or container.Annealing of the interior surface of a tube or other container may beachieved by the blowing of hot air onto said surface, the closeproximity of a source of radiant heat to the interior surface or othersuitable means familiar to those skilled in the art.

Annealing of the injection moulded thin-walled article according to thisaspect of the invention may be facilitated by one or more of a varietyof techniques. For example, the annealing step may include subjectingthe plastics material of the article to various types of electromagneticradiation, such as far infra-red, infra-red, ultra-violet and microwaveradiation. Alternatively, sonic, supersonic and/or ultrasonic energy,electrical energy, electron are, electron beam, plasma (e.g., coronaglow discharge, etc.), stream, heated gas (e.g. hot air), magneticfields, ionising radiation losers, radio frequency and direct contactwith heated or vibrating surfaces may be employed. Preferably, theannealing step is carried out by application of heat to the plasticsmaterial immediately before, during or immediately after the body isadapted to form the article.

According to a particular embodiment, the annealing process is carriedout in situ by filling the article with a medium having a sufficientlyhigh temperature to facilitate annealing of the article through thetransfer of heat from the medium to the article itself. In this case,the heated medium way be inserted before, during or immediately afterthe distortion (if any) of the article. Due to the thin-wall nature ofthe article, the temperature of the areas of the articles that come intocontact with, or are in relatively close proximity to, the medium mayassume a temperature close or equal to that of the medium itself. Forexample, although the specific area of the article that will be scaledshould preferably not come into direct contact with the medium, once themedium has been introduced into the article the temperature of the areato be sealed will tend towards that of the medium. Provided suchtemperature is high enough to initiate annealing, it will result in thepartial or complete annealing of the areas of the article, including thearea of the article to be sealed. The temperature of the in situannealing medium is preferably greater than 18° C., more preferablygreater than 22° C., even more preferably greater than 25° C., yet evenmore preferably greater than 30° C., and most preferably greater than35° C.

Alternative heat-based annealing processes include immersing the articlein, or passing the article through a bath, oven or other apparatuscontaining or able to direct at or subject the article to a warmingliquid or gas or other annealing agent. For example, the articles can beimmersed into a hot aqueous bath for sufficient time to heat them towithin the desired temperature range. The particular residence timewithin the hot aqueous bath can depend on a variety of factors such asthe shape and/or thickness of the articles and whether the aqueous bathis quiescent or agitated, whether the bath size to number of articlesresults in fluctuation of bath temperature, and other factors. Thisannealing method is particularly useful in cases where it is desirablethat the filled contents of the article are also heated above aparticular temperature, such as in retorting of some foods. The piecescan then be removed from the aqueous bath, dried and cooled to ambienttemperature.

In other preferred embodiments, radiant heating is employed, such asheating with infrared light. One advantage of radiant heating especiallywith infrared light is the rapidity with which heating step can bepriced. Still another advantage is that a separate drying step can beeliminated.

When one or more types of electromagnetic radiation is the annealingagent, an article comprised of the polymer should be exposed to theradiation for a time period at least sufficient to absorb enough energyto stress relieve the polymer against stress cracking therein. Exposuresoccurs at one or more ranges of frequencies which are capable of beingabsorbed by the polymer and which are effective for stress relievingwithout or substantially without causing heat induced softening orflowing of the polymer. The electromagnetic radiation is selected frominfrared, visible, ultraviolet, microwave, radio, loser and other typesof electromagnetic radiation.

The annealing treatment may, depending on the plastics material and thearticle, be carried out prior to, during or after the distortion of thearticle. If the annealing process is carried out prior to the distortionof the article, it is preferred that the effects of the annealingprocess an still impacting on the polymer during the distortion process.For example, if heat is used to effect annealing and the heat source isremoved or significantly reduced prior to distortion of the article, theplastics material should preferably still be sufficiently warm duringand after the distortion process to enable the annealing of thedistorted article to take place. Another method of annealing using heatis to store the final packaged product in heated or naturally warmstorage areas, the temperature in which is constantly at or periodicallyraised or allowed to rise to 22° C. or more, more preferably 25° C. ormore, yet more preferably 27° C. or more, even more preferably 30° C. ormore and most preferably 35° C. or more for sufficient time to annealthe article or part thereof as measured by an improvement in ESCR and/orGullwing tear resistance in the direction of the flow of the polymerrelative to the unannealed article or part thereof.

The entire article does not necessarily need to be annealed to achievethe beneficial effects of this aspect of the invention if desired, theannealing process can be directed to one or more areas of the article inwhich it has been determined annealing will have particularly beneficialeffects, such as those areas in the injection moulded article that aremost susceptible to ESCR or other mechanical failure. Partial annealingof the article may be achieved by, for example, annealing some parts ofthe article by eared radiation while shielding other parts of thearticle from the radiation. In the case of a tube, areas that may bebeneficially selectively annealed include the crimped/sealed andadjacent area and other areas of the tube a are distorted andconsequently have additional and unusual stresses imposed on them as aresult of the crimping/sealing process.

In addition, annealing can take place in one or more stages. Forexample, part of the article may first be subjected to annealing by, forexample, filling it with a warm fluid medium. This will anneal thoseareas of the article that are in contact with and/or close proximity tothe warm fluid medium. When the article is a tube, this initialannealing process will primarily anneal the body of the tube, althoughif the medium is sufficiently warm and sufficient time is allowed it mayalso anneal other areas of the tube, such as the area to be crimped andsealed. Subsequent to the initial annealing, and in a separateoperation, the tube may then be crimped and sealed at the open end,which will anneal this portion of the tube.

The extent of the desired annealing of a particular article can bedetermined by experimentation, and may wary depending on theextent/intensity of the deleterious effects of product to be packed intothe article on the article as well as the nature of the plasticsmaterial used to mould the article and the moulding conditions used inthe manufacture of the article and the desired properties of the treatedarticle. Particularly deleterious products (ie. with high stresscracking potential) may beneficially be packed into articles which havebeen more extensively annealed than the same article intended for usewith a less deleterious product. Similarly, articles that have higherlevels of stress due for example to their shape, the conditions of theirmanufacture and/or the extent of additional stresses posed on them dueto filling, crimping and sealing, etc. may benefit from more intensiveannealing than would otherwise be the case.

It is further noted herein that there is no limitation with respect tothe orientation of the thermoplastics to the heat sources employed.Therefore, the heat source and the thermoplastic may be moving, the heatsource may move while the thermoplastic remains stationary or viceversa.

Once heated to the desired temperature range, the article may be cooledor allowed to cool as desired. The cooling step can similarly comprisevarious cooling techniques. Especially preferred for use herein are drycooling techniques. For example, the articles can be cooled to roomtemperature with forced air convection cooling. Alternatively, thearticles can be allowed to cool naturally, i.e. without acceleratedcooling means. The air can be at room temperature or, if desired, can bechilled to shorten the cooling steps duration. In still anothervariation, ultrasonic heating can be used in substitution for theradiant heating. In still other variations, forced hot air convectionheating can be employed. The pieces can be fed into a oven or otherheating zones with various combinations of radiant and convectionheating.

The plastics material of the article according to this aspect of theinvention is not limited provided that it is capable of being injectionmoulded into a flexible thin-walled article. Indeed, preferred forms ofthe plastics material are hereafter described in accordance with furtheraspects of the invention.

In general, as described in PCT/AU99/00255, it has been found that it ispossible to injection mould flexible thin-walled articles havingrelatively long thin-walled sections by selection of the polymers usedin the injection moulding process having a time to failure of greaterthan 10 hours when tested according to the following ESCR testprocedure:

i) a plurality (preferably 6 or more) strips of the polymer or polymerblend incorporating any post moulding treatment intended for the finalarticle having the cross-sectional dimensions of 0.65 mm in thicknessand 10 mm in width arm injection moulded under high shear, long flowlength conditions, the same as or similar to those intended for use inthe manufacture of the flexible thin-walled article;ii) the strips are bent back upon themselves and stapled 3 mm from thebend;iii) the bent steps are immersed in a solution of a stress crack agentsuch as an ethoxylated nonylphenol, eg. a 10% solution of Teric; N9(nonylphenol ethoxylated with 9 moles of ethylene oxide—Orica AustraliaPty Ltd) and held at a temperature of 50° C.;iv) the strips are observed for signs of cracking, any signs of crackingare regarded as a failure; andv) the time to failure is when 50% of the strips show signs of cracking.

The ESCR test described above was developed to simulate the stressesthat are imposed on the area of a tube that is crimped and sealed afterthe comp and seal operation is carried out, this being an area of thecrimped and sealed tube that is particularly susceptible to flex andESCR failure. The need for this special test arose because ‘standard’ESCR tests such as ASTM D-1693 are totally inadequate for determiningthe ESCR of polymers when moulded into flexible thin walled mouldingsand subsequently crimped and sealed—a fact clearly illustrated by thecomparison between ESCR results on Dupont 2020T and Dowlex 2517 polymersusing a ‘standard’ ESCR test and the abovementioned test.

Generally, in order to select a polymer blend suitable for themanufacture of flexible thin-walled articles it is necessary for thepolymer blend to have an ESCR, tested according to the above procedure,of greater than 10 hours. Preferably the ESCR of the polymer blend isgreater than 100 hours, more preferably greater than 200 hours and mostpreferably greater than 360 hours. Where the thin-walled article is atube or other container used for the packaging of a composition such asa moisturiser or a shampoo which may be quite aggressive to the thinwalled article and result in a degradation of its properties over time,it is desirable to select a polymer blend having an ESCR sufficientlyhigh such that the thin walled article formed from the blend is able towithstand the rigours of use despite any degradation of propertiesresulting from the aggressive nature of the materials contained withinthe thin-walled article. Where the thin-walled article is used for thepackaging of a relatively inert material, a lower ESCR may be tolerated.

The ESCR test as hereinbefore defined may be conducted using a varietyof stress crack agents. The preferred stress crack agent is Teric N9, a9-mole ethoxylate of nonylphenol ex Orica Australia Pty Ltd. Otherethoxylates of nonylphenol may also advantageously be used. Other stresscrack agents may be used and will be selected based upon the desiredend-use, for example mineral oils, cationic surfactants, solvents andother agents which will be apparent to those skilled in the art.

The ESCR test as described above is conducted under moulding conditionsthe same as or similar to those to be used in the manufacture of thinwalled articles. For example, were it is intended to produce the thinwalled article using a moulding incorporating melt flow oscillationtechniques, it is advantageous to conduct the ESCR tests on panelsproduced from mouldings made by employing melt flow oscillationtechniques. Similarly, the moulding conditions intended for use to mouldthe thin walled articles, such as injection speed, injection pressure,melt temperature, core and cavity temperature, etc. are advantageouslyused to produce mouldings for use in the ESCR test.

The suitability of a polymer or blend for the application of the presentinvention, as well as the potential beneficial effects thereof may bedetermined by carrying out the ESCR test as described above, butpreferably with the following additions and modifications:

-   -   Prepare two sets of 6 or more strips for subjecting to the ESCR        test    -   After bending and stapling the two sets of strips, subject one        set of strips to the proposed annealing treatment (eg. an        elevated temperature of 50° C. for 30 minutes, allow the strips        to cool to 22° C.) and maintained at 22° C. for 2 hrs    -   Insert the two sets of strips in the stress crack medium as        prescribed by the ESCR test.

The potential benefit of the present invention may be assessed bycomparing the ESCR and/or Gullwing tear resistance of the polymer whentested with and without being subjected to the annealing process when inthe stressed state. The present invention is particularly applicable anduseful for walled articles where the difference in time to failure, asmeasured by the ESCR test as herein described, between annealed andunannealed strips of the polymer blend used to manufacture the articleis greater than 5 hrs, preferably greater than 10 hrs, more preferablygreater than 20 hrs, even more preferably greater than 30 hrs, morepreferably greater than 50 hrs, even more preferably greater than 100hrs and most preferably greater than 350 hrs.

Alternatively, the suitability of a polymer or blend for the applicationof the present invention may be determined by comparing the GullwingTear Resistance (measured in the direction of the flow of the polymer)of annealed and unannealed strips cut from mouldings such as may be usedin the ESCR test, such strips being of suitable dimensions for carryingout the test. Annealed strips preferably have tear resistance that ismore than 5% greater than that of unannealed strips, preferably morethan 10% greater, more preferably more than 15% greater and mostpreferably more than 20% greater. The Tear Resistance of an injectionmoulded flexible thin walled article is particularly relevant when thearticle is made of polymers that have a tendency to split or tearrelatively easily, such as polypropylene. This tendency to tear or splitis often exacerbated when the polymers are moulded into articles thatare, by the nature of the moulding process, tool design and mouldingconditions, highly orientated. The Gullwing Tear test is particularlyuseful for accessing the suitability of, amongst other polymers,polypropylene-based polymers and blends thereof (including those citedabove) for the production of injection moulded flexible thin walledarticles because such polymers and blends thereof may well pass the ESCRtest but still be unsuitable for commercial injection moulded flexiblethin walled articles because of poor tear resistance. As is noted above,annealing such articles by means of the present invention may improvetheir tear resistance to the point where the article develops commercialutility.

The benefit of the present invention is illustrated by the followingexample. A formulation consisting of 25% Profax SC973 (100 MFI PP exBasell), 34% Engage 8401 (30 MFI mPE ex Dupont-Dow) and 41% WSG 189 (100MFI LDPE ex Qenos) was moulded into 165 mm long by 0.5 mm thickcylindrical tubes under moulding conditions designed to introducemaximum stresses into the moulded tubes. The ESCR of both annealed andunannealed strips cut from tubes was assessed using the ESCR methoddescribed herein. It was found that over 60% of unannealed strips takenfrom unannealed tubes failed the ESCR test within 2 hrs, whereas nofailures were noted in the strips taken form the tubes, said stripshaving been annealed by heating the stapled strips for 30 minutes at 50°C., cooling to 22° C. and conditioning at 22° C. for 2 hrs. Further, 94%of the unannealed strips, compared to only 22% of the annealed strips,had failed by 360 hrs. This illustrates that the present inventionsignificantly improves the ESCR of injection moulded flexible thinwalled articles, and enables the use of many polymer blends that may nothave adequate ESCR when tested according to the method described hereinand which are intended for use for the manufacture of commerciallyvaluable flexible thin walled articles.

The benefits of the present invention are most noticeable in flexiblethin-walled articles having a thin section less than 1 mm in thicknessand wherein the thin section is substantially continuous for greaterthan 50 mm in the direction of flow of the molten polymer blend in themould, preferably greater than 90 mm in the direction of flow of themolten polymer blend in the mould and most preferably greater than 100mm in the direction of flow of the molten polymer blend in the mould.

Blends of isotactic polypropylene with ethylene propylene copolymershaving 4 wt. % to 35 wt. % ethylene, both components having isotacticpropylene sequences long enough to crystallize are described in WO00/01766 which is hereby incorporated by reference. Such blends may besuitable for the manufacture of flexible tubes and other containers thatare subjected to heating by such methods as heat-filling with theproduct the container is required to contain and/or heat treating thefilled container by methods such as retorting. Blends conforming to theabove specification comprise 1 wt. % to 95 wt. % of the isotacticpolypropylene and an ethylene propylene copolymer with greater than 65wt. % propylene and preferably greater than 80 wt. % propylene.

Blends of various polypropylene polymers and ethylene, propylene orbutene α-olefin polymers may also be particularly suitable for themanufacture of flexible tubes and other containers that are subjected toheating by such methods as heat-filling with the product the containeris required to contain and/or heat treating the filled container bymethods such as retorting. Blends conforming to the above specificationcomprise component (a) at least one isotactic, syndiotactic or atacticpolypropylene homopolymer or α-olefin copolymer, preferably one or moreof a C₂ to C₂₀ α-olefin copolymer, more preferably one or more of a C₂to C₈ α-olefin copolymer made with a variety of catalysts such asmetallocene or similar catalysts, and component (b) at least one of anethylene, propylene and/or butene copolymer, preferably a C₂ to C₂₀α-olefin ethylene, propylene or butene copolymer, more preferably a C₂to C₈ α-olefin ethylene copolymer made with a variety of catalysts suchas metallocene or similar catalysts and featuring a super-randomdistribution of the copolymer within and amongst the molecular chains ofthe polymer. The blends consist of 1% to 99% of component (a) and 99% to1% of component (b), preferably 30% to 99% of component (a) and 70% to1% of component (b), even more preferably 45% to 99% of component (a)and 55% to 1% of component (b), yet more preferably 55% to 99% ofcomponent (a) and 45% to 1% of component (b), and most preferably 60% to99% of component (a) and 40% to 1% of component (b).

As is noted in PCT/AU98/00255, AU 200020674 A1, AU 72146-99, AustralianInnovation Patent No 2002200093 and Australian Innovation Patent2002100211, all of which are hereby incorporated by reference, blendingat least one compatible agent with at least one polymer frequently hasthe effect of substantially improving the ESCR. Such incorporation of acompatible agent also frequently improves the Gullwing tear test of theblend. The at least one compatible agent is preferably a polymer (alsoreferred to herein as a ‘compatible polymer’) and when blended with theat least one polymer results in blends having properties which, whenused to mould flexible thin-walled articles such as flexible injectionmoulded tubes, are superior to the original constituents or the neatpolymers. This phenomenon is advantageously used to formulate blendssuitable for the reaction moulding of the flexible tin walled articlesof the invention.

A particular class of compatible agents have been found by the applicantto be particularly useful in blends for the manufacture of flexiblethin-walled articles by injection moulding. Those are high melt flowcompatible polymers. It has been found that blends including suchcompatible agents are particularly useful in the process described abovein relation to the first aspect of the invention, and may also be usefulin processes that do not include the above described annealing of thearticle formed.

Therefore, according to a second aspect of the invention there isprovided a process for the manufacture of flexible thin-walled articlescomprising injection moulding a blend of (a) at least one polymer and(b) at least one high melt flow compatible polymer having an MFI ofgreater than 100.

It will be appreciated that the following discussion of the blendsaccording to the second aspect of the invention will be equallyapplicable to the processes of the first aspect of the invention.

The high melt flow compatible polymer has an MFI of greater than 100,preferably greater than 200, more preferably greater than 300, and mayhave an MFI of greater than 500, still further greater than 1000 and yetfurther greater than 1,500. One or more of the polymer components ofeither or both (a) and (b) are advantageously produced with ametallocene or similar catalyst system.

In the polymer blend, component (a) is preferably about 40 to about 99.9weight percent of the blend based on the total weight of (a) and (b) andforms the continuous or co-continuous phase of the blend. The polymerblend is generally formed by mixing blend components (a) and (b) underhigh shear mixing conditions or other means capable of producing anintimate mix, such as in parallel or series reactors, each reactorproducing one or more components of blend components a) and/or b). Aunit such as a twin-screw extruder would be an example of a suitablepiece of mixing equipment. Other areas to achieve a well mixed blendwill be apparent to those skilled in the art.

The polymer blend may be prepared by extrusion of some or alt of thecomponents of the polymer blend and the resulting extrusion chopped andused in the injection moulding process of the present invention.Alternatively, the polymer blend may be provided in its component formand subjected to mixing before and during the melting of the polymerblend in the present process.

The high melt flow compatible polymer may be selected from the groupconsisting of ethylene vinyl acetate; ethylene, vinyl alcohol;plasticised polyvinyl acetate and polyvinyl alcohol; alkyl carboxylsubstituted polyolefins; copolymers of anhydrides of organic acids;epoxy group containing copolymers; chlorinated polyethylene;ethylene-propylene-butylene etc. copolymers; ultra low density, very lowdensity, low density, medium density and high density polyethylene andcopolymers thereof; polypropylene, polybutylene and copolymers thereof;polyester ethers; polyether-esters (such as DuPont's Hytrel range);acrylonitrile-methacrylate copolymers; block copolymers having styreneend blocks; half esters; amino and alkoxysilane grafted polyethylenes;vinyl addition polymers; styrene-butadiene block copolymers; acidgrafted polyolefins; vinyl pyrrolidine grafted polyolefins; blockcopolymers of dihydric monomers; propylene graft unsaturated esters;modified polyolefins comprising amide, epoxy, hydroxy or C₂-C₆ acyloxyfunctional groups; other polymeric compatibilisers suitable for use withpolyolefins; particles coated with any of the above; and mixturesthereof. In the above compatible polymers the functional groups aregenerally incorporated into the modified polyolefin as part of anunsaturated monomer which is either copolymerised with an olefin monomeror grafted onto a polyolefin to form the modified polyolefin. Includedare ethyl and/or methyl acrylates of ethylene and/or propylene, andethylene acrylic acid and methacrylic acid copolymer resins.

Also included are blends of compatible polymers, such as a neutralisedionomer such as a Surlyn (Dupont) and EEA and/or EMA and/or EMAA. Forexample, a low MFI partly neutralised ionomer such as Surlyn 9970(MFI=14) may be compounded with a high MFI EMA such as Nucrel 599(Dupont) (MFI=500) to achieve a compatible polymer blend with a higherMFI than is achievable with the Surlyn alone, while still being able tobenefit from the beneficial properties of the Surlyn. Those skilled inthe ad will appreciate that the above example is but one of a very widevariety of combinations of compatible polymers that are covered by thepresent invention.

Alkyl carboxyl substituted polyolefins may include substitutedpolyolefins where the carboxyl groups are derived from acids, esters,anhydrides and salts thereof. Caboxylic salts include neutralisedcarboxylic acids and are often referred to as ionomers (eg. Surlyn).Typically acids, anhydrides and esters include methacrylic acid, acrylicacid, ethacrylic acid, glysidyl maleate, 2-hydroxyacrylate, diethylmaleate, maleic anhydride, maleic acid, esters of dicarboxylic acids,etc. Preferred examples include ethylenically unsaturated carboxylicacid copolymer such as polyethylene methacrylic acid and polyethyleneacrylic acid and salts thereof. Copolymers of anhydrides of organicacids include copolymers of maleic anhydride as well as copolymers ofcyclic anhydrides.

Poly-2-oxazoline compounds and fluoroelastomers are also suited for useas a high melt flow compatible polymer. Incorporation of 1-40%, mostpreferably 2-20% of poly-2-oxazoline compounds is preferred. Thesecompatible polymers improve the adhesion of the PE blend to varioussubstrates, which may make them useful for printing or labelling. Thecompatibilizing polymer comprises an α-olefin copolymer substrategrafted with amounts of monovinylidene aromatic polymer. Preferably, theα-olefin copolymer substrate is a terpolymer of ethylene, propylene anda non-conjugated diolefin. Particularly useful as compatible polymersand high MFI compatible polymers are various aromatic/aliphatic olefincopolymers of which styrene-1,4-butadiene-butylene-styrene bockcopolymers (SBBSA copolymers), styrene-butadiene-styrene copolymers (SBScopolymers) and styrene-ethylene-butylene-styrene copolymer (SEBScopolymers) are particularly useful examples for the production offlexible thin walled articles.

The high melt flow compatible polymer of the second aspect of thepresent invention is a compatible polymer or a mixture thereof whereinat least one compatible polymer generally has an MFI of greater than100, preferably greater than 200, more preferably greater than 300, andpotentially greater tin 500, or greater than 1,000, or still furthergreater than 1500. Unless otherwise stated, MFI is measured according toASTM D 1238 (Condition 190° C./2.16 kg). Unless otherwise stated, theMFI of polymers in which propylene constitutes over 50% of the weightunits of the polymer are measured by ASTM D 1238 at 230° C., 2.16 kg.Preferably the high melt flow compatible polymer of the presentinvention is a polypropylene homopolymer, a block or random co ortetrapolymer of polypropylene, or a mixture thereof, wherein thepropylene-based polymer component has an MFI (as measured by ASTM D 1238at 230° C., 2.16 kg) of 100 g/10 min or more, often greater than 200,sometimes greater than 300, and even greater than 1500. Preferably thepropylene-based polymer component is an isotactic or syndiotacticpolypropylene homopolymer or copolymer having a MFI falling within theranges specified above. Preferably the propylene-based polymer componentwill have a MWD of from 1.8 to 4.0 and a narrow composition distributionthat is characteristic of metallocene or similar catalysed propylenepolymer. However, propylene-based polymers such as are cited in U.S.Pat. No. 6,476,173 and which is incorporated herein by reference andwhich have MWDs up to 20 will often produce good results. Polymers suchas are cited above are conveniently produced using a stereospecificmetallocene catalyst system. Random ethylene/propylene/vinyl aromaticinterpolymers such as ethylene/propylene/styrene interpolymers may alsobe used as the compatible and/or high melt flow compatible polymer inthe present invention. Polymers having similar specifications to thosedescribed above but having Mars less that 100 are also useful ascompatible polymers of the present invention.

A wide variety of polypropylene-based high melt flow compatiblepolymers, particularly when blended with low molecular weightplastomers, substantially linear polyethylenes, metallocene long-chainbranched polyethylenes and copolymers of the aforementioned ethylenepolymers as the polymer, will produce blends suitable for use in theprocess of the present invention. Many monomers have been copolymerizedwith propylene to form copolymers of propylene for use as compatiblepolymers. Many high MFI grades of these copolymers are suitable as thepolymer or compatible polymers for use in the present invention.

High MFI polypropylenes suitable as a high melt flow compatible polymerfor use in the process of the present invention include isotactic,sydiotactic and atactic polypropylene and blends thereof of variousMFIs, densities and crystallinities as would produce desired propertiesin products moulded by the process of the present invention,Polypropylenes particularly useful as the high melt flow compatiblepolymer include homopolymers or copolymers of propylene and one or moreα-olefins selected from ethylene or linear or branched C₄ to C₂₀α-olefines, preferably ethylene or C₄ to C₈ α-olefins, more preferablyethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene,3,5,5-trimethyl-1-hexene, and 1-octene, even more preferably ethylene or1-butene or hexene or octene, and optionally, minor amounts ofnon-conjugated diolefins, preferably C₆-C₂₀ diolefins. In oneembodiment, the α-olefin ca contain cyclic structures that are fullysaturated such that the α-olefin monomer does not contain a cyclicmoiety with any olefinic unsaturation or any aromatic structures.Preferred α-olefins are mono-olefins. These propylene copolymers withprescribed range of comonomer levels are preferably prepared bypolymerization of the suitable olefins in the presence of supported orunsupported metallocene or similar catalyst systems.

When the propylene-based compatible polymer either consists of orcontains one or more copolymers, such copolymers are preferably composedof propylene as a main monomer and an α-olefin other than propylene asthe co-monomer. The content of the propylene is generally 70 molepercent or more, often 80 mole % or more, frequently 90 mole % or moreand sometimes 98 mole % or more. The polypropylene copolymer of thepresent invention preferably comprises a random crystallisable copolymerhaving a narrow compositional distribution such as can be produced bymetallocene or the like catalysts.

Many copolymers of ethylene are also useful as high melt flow compatiblepolymers in the process of the present invention. For example singlesite catalysed polymers such a metallocene catalysed polyethylene andethylene.

The polymer blends preferably include (a) at least one polymer having anMFI of greater than 10, preferably greater than 20, more preferablygreater than 30, even more preferably greater than 50, the polymerpreferably being an ethylene or propylene or butene homo or α-olefininterpolymer and preferably produced with a metallocene or similarcatalyst which will display narrow composition distribution, meaningthat the fractional comonomer content from molecule to molecule will besimilar; and (b) at least one high melt flow compatible polymer,preferably an ethylene, propylene or butene homo or α-olefininterpolymer having a melt flow rate of greater than 100 and preferablyproduced using a metallocene or similar catalyst. All references tometallocene catalysts shall include other catalysts (e.g. single-siteand geometry catalysts) capable of producing polymers having propertiesthe same as or similar to metallocene-produced polymers (e.g. narrow orbroad MWD, narrow composition distribution). Such blends can optionallyinclude additives well known tot those skilled in the art, and mayinclude amongst others, additives that reduce the water vapour and/oroxygen transmission rates of the polymers in which they areincorporated. For example, and as described in WO/02/074854 which isincorporated by references the addition of between 0.5% and 3% of a lowMW hydrogenated aliphatic resin such as poly(dicyclopentadiene) mayreduce the normalised moisture vapour transmission and sometimes the O₂transmission rate of the blend and articles made therefrom.

Polyethylene, as used herein, can be a homopolymer or a copolymer andincludes ethylene plastomers, VLDPE, LLDPE, LDPE, and HDPE, Ethyleneplastomers, as used herein, refers generally to a class of ethylenebased copolymers with density of less than about 0.915 g/cc (down toabout 0.865 g/cc). Ethylene plastomers have an ethylene crystallinitybetween plastics (i.e. linear low density and very low densitypolyethylenes) and ethylene/α-olefin elastomer. VLDPE is very lowdensity polyethylene, typically having a density in the range of from0.90 to 0.915 g/cc. LLDPE is linear low density polyethylene, typicallybasing a density in the range of from 0.915 to 0.930 g/cc. LDPE is lowdensity polyethylene, typically having a density in the range of from0.915 to 0.930 g/cc. HDPE is high density polyethylene, typically havinga density in the range of from 0.930 to 0.970 g/cc.

Although PCT/AU98/00255 advises that “a wide variety of polypropylenepolymers possessing a very wide range of MFIs (1-200+), densities andcrystallinities will produce blends suitable for use is the process ofthe present invention”, it does not describe any particular advantagesto be derived from the incorporation of at least one compatible polymerof any nature, including polypropylene polymers, with high MFIs, andindeed gives no examples of compatible polymers with an MFI greater than100.

The compatible polymer largely forms the disperse or co-continuous phaseof the blends of the present invention. It has now been found that,surprisingly, the incorporation of at least one high melt flowcompatible polymer in formulations for the manufacture of a flexible tinwalled article frequently has a number of significant advantagesrelative to the use of the same compatible polymer(s) but with a lowMFI. It has also been found that provided the molecular weight of the atleast one compatible polymer doesn't fall below a value beyond which itsability to improve the ESCR and/or tear strength in the direction of thepolymer flow of the moulded blend is negated, the incorporation of highMFI compatible polymers into the blend has a number of significantadvantages relative to the incorporation of low MFI grades of the samecompatible polymer. For example, the high melt flow compatible polymerfrequently has the effect of increasing the shear sensitivity andoverall MFI of the whole blend, thereby improving its flow properties.Also, because there is usually an inverse relationship between MFI andsome physical properties of polymers, it is frequently found thatpolymer properties such as flex modulus and hardness decrease withincreasing MFI. When it is desired, for example for reasons of cost ESCReffectiveness, etc., to use as a particular compatible polymer, but thelow MFI grades of that polymer (i.e. polymers with MFIs≦100) have a flexmodulus that is too high relative to the desired application and whichresults in mouldings and that are too stiff, the substitution of a highMFI chemically similar or identical compatible polymer for all or partof the compatible polymer with an MFI of ≦100 in a blend enables theproduction and use of blends with much higher MFI than were previouslyattainable while at the same time reducing the adverse impact onproperties such as ‘feel’ and higher flex modulus that would normally beassociated with lower MFI grades of the compatible polymer. Depending onthe desired properties of the moulded article, the high melt flowcompatible polymer can be used either as the sole compatible polymer ina blend or may be blended with other MFI compatible polymers, which maybe either high or low MFI compatible polymers.

Without wishing to be bound by theory, it is believed that theinteraction between the polymer and the compatible polymers andparticularly a high melt flow compatible polymer forms regions withinthe moulded articles which can be regarded as “joints”. These “joints”appear to absorb or disperse stress in articles made from the polymerblend. The presence of these “joints” interspersed within the articleappears to absorb or dissipate the stresses within the article whichwould otherwise result in decreased physical properties. It is believedthat the benefits obtained form the use of at least one high melt flowcompatible polymer are due primarily to their being more effectivelydispersed in the at least one compatible polymer relative to lower MFIversions of the same compatible polymer and that they enable theformation of more and, smaller disperse phase particles sizes relativeto that enable with low MFI versions of the same polymer. In general,the higher the MFI of the compatible polymer, the smaller the particlesize that it can form, although there will be an MFI (and hence MW)beyond which reducing the MW further will not resulting furtherreductions in high melt flow compatible polymer particle size. Thesmaller particle size of the disperse phase in turn results in anincrease of the total surface area of a given weight percentage of thecompatible polymer, thereby enabling a greater number of joints andareas of interaction between the polymer and the disperse phase (i.e.the compatible polymer) of the blend. The effect of reducing theparticle size of a compatible polymer on the number of particles of thecompatible polymer in the blend is illustrated by the fact that for agiven weight % of a compatible polymer in a blend, halving the particlesize (eg. by halving the particle radius) of the compatible polymerincreases the number of compatible polymer particles by a factor of 8and the total surface area of the compatible polymer by a factor of 2.Thus halving the radius of the particles of compatible polymer increasesthe number of stress-relieving ‘joints’ within the moulding by a factorof 8 and the surface area of the interface between the compatiblepolymer and the polymer by a factor of 2. Both these increases have thepotential effect of improving moulding properties such as ESCR and tearstrength.

Again without wishing to be bound by theory, we believe that theincrease in particle numbers and surface area of the compatible polymerof the discontinuous phase is one of the key reasons for many of theproperty improvements (eg, ESCR, tear strength) of the invention. Theimprovements in ESCR etc. resulting from the incorporation of high MFIcompatible polymers open enables the percentage of compatible polymer ina blend to be reduced while still attaining an acceptable ESCR etc. Thismay be advantageous, for example where it is desirable to reduce theamount of a polypropylene compatible polymer in a blend in order toreduce the flex modulus of said blend. Alternatively, and using the sameexample, maintaining the weight % of the high melt flow compatiblepolypropylene results in significant increase in the number of dispersephase particles relative to a low MFI equivalent polypropylene which inturn increases the overall ESCR of the blend. This ESCR improvement inturn enables the use of higher MFI polymers, thereby increasing theblend's processing characteristics while maintaining acceptable ESCRperformance.

Without wishing to be bound by theory, we believe that the interfacialtension between two miscible polymers decreases with decreasingmolecular weight, so that as the MFI of the disperse phase increases sodoes the compatibility between the polymers until they become miscible.For each type of compatible polymer there will be an upper limit on howhigh it's MFI (i.e. how low its molecular weight) can be before itstarts to unacceptably degrade the performance of a particular blend foruse in a particular application. This upper limit will vary, dependingon the characteristics of the particular compatible polymer (e.g.homopolymer or copolymer PP, ionomer etc.), the properties of any othercompatible polymers in the blend as well as the characteristics of thepolymer(s) and the interaction between them as well as the end use ofthe moulded product (eg. what is intended to be packed into theproduct), and can be determined by experimentation. For someapplications some degradation of some characteristics of a particularblend due to the incorporation of one or more high MFI compatiblepolymers relative to the same blend but with a low MFI version of thesame compatible polymer may be acceptable in order to achieve thebenefits of the improvement of other properties of the blend that resultfrom their incorporation. Again, the limits on how high the MFI of thehigh melt flow compatible polymer can be as well as the level ofincorporation that can achieved before the blend performance is degradedto an unacceptable level can be determined by experiment.

The high melt flow compatible polymer may be directly produced in areactor using appropriate catalysts (including metallocenes or similarcatalysts) and processing conditions. The high melt flow compatiblepolymer may also be prepared by ‘cracking’ lower MFI polymers of thesame type by means of various peroxides or other molecular chain-cuttingpolymers known to those skilled in the art. For example, a 50 MFIpolypropylene homopolymer or copolymer may be converted into a high MFI(e.g. a 300, 500, 1,000 or 1500 MFI) polypropylene homopolymer orcopolymer by means of cracking it. The cracking required to produce ahigh melt flow compatible polymer of a particular MFI can be achievedprior to incorporation of the high melt flow compatible polymer into thepolymer, thereby producing a high melt flow compatible polymer ready forincorporation into the blend. Alternatively, the high melt flowcompatible polymer may be produced in situ in the blend by incorporatinginto and/or coating the compatible polymer with an appropriate amountand type of a cracking agent capable of cracking the polymer to therequired MFI, adding the thus prepared compatible polymer/cracking agentcombination to one or more of the other blend components and processingthe resultant blend under conditions (usually a high enough temperature)sufficient to enable the cracking agent to reduce the MW (molecularweight) of the compatible polymer to a level that will result in thedesired MFI of the compatible polymer. If this latter method ofachieving the high melt flow compatible polymer is used, it is necessaryto assess the impact, if any, of the cracking agent on the other blendcomponents during processing (ie. to assess for any unintended crackingor cross-linking of the other blend components by the cracking agent),and if necessary to adjust the blend formulation to correct for theconsequences of these effects on the overall properties of the blond. Afurther method of producing blends of the present invention containing ahigh melt flow compatible polymer as the disperse phase within acontinuous or continuous phase of a polymer is to produce a reactorblend of the high melt flow compatible polymer and polymer. This may beachieved by a number of means that are known to those skilled in theart. For example, the high melt flow compatible polymer and polymer maybe produced in a single reactor in the presence of appropriatecatalysts. Alternatively they may be produced in parallel or series intwo or more reactors, or one polymerized component may be added in itsfinished state a reactor in which the other component is being produced.

Some preferred properties of the final composition when moulded includehigh tensile strength, flexibility and tear strength. The extractablescontent for the compositions of the invention and mouldings therefrom ispreferably less than or equal to 2.0 wt %, more preferably less than orequal to 1.6 wt %, most preferably less than or equal to 1.4 wt % asmeasured by ASTM D-5227.

Similar to the function of compatible agents as described inPCT/AU98/00255, the high melt flow compatible polymer of this aspect ofthe present invention is used in an amount at least sufficient toimprove the environmental stress crack resistance and/or tearresistance, as measured by the Gullwing tear test, of the polymer blend.The high melt flow compatible polymer may also be used in amounts inexcess of those requested to compatibility the polymer blend in order toimprove the viscosity characteristics of said polymer blend so as tooptimise the moulding characteristics of said polymer blend and/orgeneral properties of the moulded product such as softness andflexibility. Typically, the high melt flow compatible polymer is used inan amount of from about 2 to about 40 weight percent of the polymerblind, although lower or higher amounts may be used in certain polymerblends. The optimum amount for a specific formulation will depend on theproperties required and can be determined by experimentation. Further ithas been found that inclusion of percentages of high melt flowcompatible polymers that are greater than necessary for increasing theenvironmental stress crack resistance of the polymer blend will oftenalso enable the improvement of the polymer blend properties such as tearand impact strength, barrier properties, chemical resistance, processingand product feel. For example, the incorporation of greater thannecessary percentages of a polypropylene-based high melt flow compatiblepolymer to improve the environmental stress crack resistance of apolyethylene-based polymer blend to the desired level may improve thechemical resistance and general barrier properties, and reduce the watervapour and water transmission rate of the polymer blend compared topolymer blends containing the minimum amount of polypropylene-based highmelt flow compatible polymer required to improve the environmentalstress crack resistance only. The properties of such blends of the highmelt flow compatible polymer of the present invention may further bemodified by the selection of suitable grades of the high melt flowcompatible polymer and/or the polymer components to achieve the desiredfinal properties. For example, where it is desired to have a polymerblend containing a relatively high percentage of polypropylene-basedpolymers, blend properties such as the ‘feel’, ‘softness’, impactresistance (especially low-temperature impact resistance),elongation-to-break, tear resistance and/or irritability of such a blendmay be substantially modified by utilising a relatively low percentageof low-flex-modulus polymers as the polyethylene-based components of theblend. Examples of suitable low-flex-modulus polyethylene-based polymersinclude low flex modulus plastomers such as DuPont-Dow Engage 8401plastomer and some of Mitsui's Tafmer XR propylene/α-olefin copolymers.Further, it has been found that the inclusion of greater than necessarypercentages of the high melt flow compatible polymer may enable theincorporation of greater percentages of other polymers than wouldotherwise be consistent with this invention. Thus, using the high meltflow compatible polymer in such quantities may enable the incorporationof greater-than-otherwise-possible amounts of such beneficial,essentially incompatible other polymers such as nylons and EVOH, withconcomitant improvements in properties such as tear and impact strength,barrier properties, chemical resistance and product feel.

The high melt flow compatible polymer containing polymer blend may alsoincorporate a variety of other additives. Examples of additionaladditives include further polymers, slip agents, anti-tack agents,pigments, dyes, filers, antioxidants, plasticisers, UV protection,viscosity modifying polymers, additives (some of which may themselves bepolymers) capable of reacting with or absorbing deleterious chemicalssuch as oxygen and other mould release polymers and melt strengthmodifiers amongst others. Additionally, compatibilisers that improvevarious properties of the blends, such as weld line strength,compatibility between the polymer and high melt flow compatible polymer,disperse phase particle size reduction, ESCR, tear strength, etc., maybe added to the blends. The abovementioned and other suitable additivesmay be added to one or more components of the polymer blend or thepolymer blend as a whole prior to moulding in order to modify itsproperties to suit specific applications or to achieve specific effectsin the end product. In cases where one or more of the additives isitself a polymer, for example in the case of some oxygen-scavengingsystems, said polymer may be the polymer or compatible polymer of thepolymer blend. Non-polymer additives may be compatible polymers of thepolymer blend.

A wide variety of polymers may be used as the polymer in blends with thehigh melt flow compatible polymer of the present invention. Thesepolymers include olefin homopolymers and copolymers, preferably ethyleneor propylene or butene homopolymers and copolymers with C₃-C₂₀ α or betaolefins and/or polymers, preferably C₃-C₈ α or beta olefins, suchpolymers having densities ranging from very low to high density (densityranges between 0.85 and 0.97 g/cm³). Also suitable for use in thepresent invention are ethylene, propylene and butene copolymers withterminal vinyl groups and ethylene, propylene and butene copolymerscontaining greater than 50% ethylene, propylene or butene which arecopolymerised with comonomers such as methyl acrylates, ethyl acrylates,acrylic acid, methacrylic acid and other polar comonomers, ionomers,styrene-ethylene/butene-styrene ABA copolymers, styrene, halo- or alkylsubstituted styrenes or other vinylidene aromatic monomers and/or one ormore hundred aliphatic or cycloaliphatic vinylidene monomers,tetrafluoroethylene, vinylbenzocyclobutane, and naphthenics (e.g.,cyclopentene, cyclohexene and cyclooctene). These polymers may be madeby a wide variety of methods including high and low pressure processes,using a wide variety of catalysts such as Ziegler-Natta andmetallocenes, and have molecular structures ranging from linear tohighly branched, thus included are LDPE, MDPE and HDPE. Particularlysuitable for use in the present invention are plastomers, ‘substantiallylinear’ and branched polyethylenes or polypropylenes, copolymers ofpropylene and ethylene or one or more α-olefins, terpolymers ofethylene, propylene and one or more α-olefin (of which Montell'sCatalloy polymers are an example) and polymers and copolymers ofpropylene manufactured using metallocene or similar catalysts and whichare characterized by a super random distribution of the copolymers.Random propylene copolymers are suitable for the production of flexiblethin-walled mouldings, particularly when improved optical clarity isrequired. Other polymers suitable for use in the present inversioninclude polylactic acid polymers, other suitable biodegradable polymersand polyketones, ethylene carbon monoxide copolymers (ECO),ethylene/propylene carbon monoxide polymers (EPCO), linear alternatingECO copolymers such as those disclosed by U.S. Ser. No. 08/009,198, thedisclosure of which is incorporated herein by reference, recycledpolyethylene (e.g., post consumer recycled high density polyethylenerecovered from waste bottles).

As exemplified in JP 07316356, JP 07316355 and JP 07330982 which areincorporated herein by reference, blends of crystalline PP incombination with ethylene/styrene/α-olefin elastomers may be suitable asa polymer for the production of flexible thin walled articles.

Also suitable for use as polymers are linear or branched isotacticpolymers, particularly polypropylene and polybutene homopolymers orrandom copolymers which have a structure in which their tacticity varieswithin the range of between 25 and 60% of [mmmm] pentad concentration.This variation in tacticity is due to the statistic distribution ofstereoscopic errors in the polymer chains. Such polymers are describedin, amongst others, WO 01/27169 (P&G), WO/99/52955 (Ringer) and WO99/52950 and (Rieger) which are hereby incorporated by reference. Theterm “stereoscopic error” refers to a stereoscopic sequence, typicallybut not exclusively characterized by a [mrrm] pentad, which has beenintroduced into a polymer in which a different pentad (eg. [mmmm](isotactic) or [mrmr] (syndiotactic) characterises the polymer. Thesestereoscopic errors change the characteristics of the polymer—forexample, an isotactic PP with stereoscopic errors tends to have moreelastomeric properties than the same polymer without stereoscopicerrors. The term “tacticity” is measure of the orderliness of thesuccession of configurational repeating units in the main and/or sidechains of a polymer molecule.

Also suitable for use in the present invention are linear or branchedisotactic polymers having an arbitrary or rather regular sequence ofisotactic and atactic blocks within the polymer molecules, such as aredescribed in WO/99/29749 (ExxonMobil), which is hereby incorporated byreference. WO/99/2949 describes a branched polyolefin having crystallinesidechains and an amorphous backbone wherein at least 90 mole percent ofthe sidechains are isotactic or syndiotactic polypropylene and at least80 mole percent of the backbone is atactic polypropylene.

Polymers with reduced tacticity such as are described above may haveparticular utility in blends as at least one compatible polymers inblends in which the at least one polymer is a crystalline orsemi-crystalline PP. This will be particularly the case when thepolymer(s) in question has a relatively low flex modulus as it acts toreduce the flex modulus of the blend with a crystalline orsemi-crystalline PP at least one polymer, and increasing the tearresistance flex modulus and impact resistance of the blend.

Recent developments in polypropylene polymerisation technology haveapplication for injection moulded flexible thin walled mouldings. Onesuch development is the ability to produce very flexible, soft andelastic polypropylene polymers with minor percentage of ethylenecopolymer and essentially no diene. These polymers have limitedcrystallinity due to adjacent isotactic propylene units and have arelatively low melting point. They are generally devoid of anysubstantial intermolecular heterogeneity in tacticity and comonomercomposition, and are substantially free of diene. They are also devoidof any substantial heterogeneity in intramolecular compositiondistribution. The ethylene copolymer includes lower limit of 5% byweight ethylene-derived units to an upper limit of 25% by weightethylene-derived units. Within these ranges, these copolymers are mildlycrystalline as measured by differential scanning calorimetry (DSC), andare exceptionally soft, while still retaining substantial tensilestrength and elasticity. Such polymers are described in U.S. Pat. No.6,525,157 (ExxonMobil).

Recent developments have resulted in the synthesis of partially atactic,partially isotactic polypropylene polymers which have elastomericproperties. It is believed that in these components each moleculeconsists of portions which are isotactic, and therefore crystalline,while the other portions of the same polypropylene molecule are atacticand therefore amorphous. Such polymers are be suitable for injectionmolded flexible thin walled mouldings, either as the at least onepolymer or the at least one compatible polymer in blends combinationswith other polymers, such as polyethylenes, polypropylenes and/orα-olefin copolymers thereof. Examples of these propylene homopolymerscontaining different levels of isotacticity in different portions of themolecule are described by in, amongst others, U.S. Pat. No. 5,594,080(Waymouth), in Journal American Chemical Society (1995), Vol. 117, page11586, and in the Journal American Chemical Society (1997). Vol. 119,page 3635.

Especially when polymers such as are described in the P&G, Rieger,Waymouth and ExxonMobil patents are incorporated in blends having havean MFI greater than 10, preferably greater than 20 more preferablygreater than 30 and most preferably greater than 50, and still morepreferably the polymers themselves have an MFI greater than 10,preferably greater than 20 more preferably greater than 30 and mostpreferably great than 50, they may be used either as the sole polymer oras a compatible polymer or high melt flow compatible polymer and mayhave either narrow or broad molecular weight distribution. Polymers suchas may have described above are often particularly to the production offlexible thin walled articles relative to the equivalent polymers ofhigher tacticity because their relatively reduced tacticity results inpolymers with reduced rigidity an increased flexibility and elasticity.If the polymer(s) is used as a compatible polymer or high melt flowcompatible polymer, it is advantageous, though not necessary, that it isused in conjunction with at least one polymer that is made from the samemonomer(s) as the compatible polymer or high welt flow compatiblepolymer because this results in greater compatibility/stability betweenthe polymer(s) as well as allowing for easier recycling of injectionmoulded flexible thin walled articles produced from such blends. Forexample, if the polymer is a polypropylene homopolymer or copolymer withtacticity varying between 25 and 60% of [mmmm] pentad concentration, itcan be blended with a polypropylene homopolymer or copolymer with ahigher tacticity to produce a blend suitable for use in flexible thinwalled articles. Alternatively, these polymers may be used inconjunction with other polymers to form blends that art suitable for useto manufacture flexible injection moulded thin walled articles. Forexample, these polymers may be blended with polyethylenes and copolymersof different types, including LDPE, MDPE and HDPE, which in turn may bemanufactured using a variety of different manufacture, techniques,catalysts and copolymers such as are described in PCT/AU98/00255 andherein. Preferably, the polyethylene is manufactured using metalloceneor similar catalysts.

In many blends suitable for the present invention, it is advantageous toincorporate at least two polymers into blends, with at least one polymerhaving a higher crystallinity, and preferably a higher MFI, than the atleast one other polymer. It is preferable, though not essential, thatthe higher crystallinity polymer has a crystallinity that is at least 5%greater, and preferably 10% or more greater than the crystallinity ofthe at least one other polymer. The high crystallinity polymer may bemade by a variety of methods using a variety of catalysts includingmetallocene, Ziegler Natta, constrained geometry catalysts, or may beproduced by a free radical reaction process, and may be linear,substantially linear or branched in structure. In blends in which a highcrystallinity polymer is incorporated with an at lest one lowercrystallinity polymer (which is preferably a metallocene polymer),better ESCR results are often obtained when the high crystallinitypolymer has a broad MWD (molecular weight distribution). A broad MWD(i.e. multi modal) high crystallinity polymer can be produced by avariety of methods. These include:

-   1) Intimately blending two or more polymers having different MFIs in    appropriate blending equipment;-   2) Producing bi or multi modal polymers by means of ‘tandem’    reactors; and-   3) Producing bi or multi modal polymers in a single reactor using    appropriate catalysts.

We have found that plastomers, substantially linear polyethylenes,metallocene branched polyethylenes and copolymers of the aforementionedethylene polymers, propylene α-olefin interpolymers and metallocenepropylene polymers and interpolymers are preferred polymers for use inthe present invention for the production of thin-walled products, andespecially for the production of flexible thin walled articles. A keycharacterised of plastomers, substantially linear polyethylenesmetallocene branched polyethylenes and copolymers of the aforementionedethylene polymers, propylene α-olefin interpolymers and metallocenepropylene polymers and interpolymers is their composition distributionthe uniformity of distribution of comonomer within and among themolecules of the polymer. Another advantage of such catalysts is thatthe degree of molecular branch within and between the molecules of thepolymers produced by them is more uniform than is obtained usingconventional catalysts. For example, convention Ziegler-Natta catalystsgenerally yield copolymers having a considerably broader compositiondistribution—and in the case of copolymers the comonomer distribution inpolymers thus produced will vary widely among the polymer molecules, andwill also be less randomly distributed within a given molecule. Also,the degree of long chain branch is more consistent between moleculesproduced by metallocene or similar catalysts than are produced by Z—N orsimilar catalysts.

These polymers may advantageously have a molecular weight distributionin a ratio Mw/Mn range of 1.5-30, preferably in the range of 1.8-10 andmore preferably in the rouge 2-4. Generally, plastomer, substantiallylinear or branched ethylene or propylene polymers comprise ethylene orpropylene homopolymers and interpolymers of ethylene and/or propylene,with at least one C₃-C₂₀ α-olefin copolymer being especially preferred.The term “interpolymer” is used herein to indicate a copolymer or a terpolymer or the like. That is, at least one other comonomer iscopolymerised with ethylene or propylene to make the interpolymerα-olefins.

When the polymer is a plastomer, substantially linear or branchedpolymer in which propylene or butene constitutes over 50% of thepolymer, the MFI of the propylene or butene α-olefin copolymer may behigher thin is generally acceptable for flexible thin-walled injectionmoulded articles when ethylene α-olefins constitute the polymer, due topropylene and butene α-olefins generally possessing better inherent ESCRproperties at the same MFI compared to most ethylene α-olefins. Thus,many propylene and butene α-olefins, particularly those prepared bymetallocene or similar catalysts, can have MFIs up to and greater than200 and still produce acceptable flexible thin walled articles with goodESCR when used as the at least one polymer and/or at least on compatiblepolymer. The optimum MFI for a particular propylene or butene α-olefinpolymer can be determined by experimentation by one skilled in the art,but will preferably be >30, more preferably >50, and generally >100 andpossibly >150. α-olefins suitable for copolymerisation with propylene orbutene to produce propylene or butene α-olefins suitable for the presentinvention include α-olefins in the range of about 2 to about 20 carbonatoms, preferably in the range of about 3-16 carbons, most preferably inthe range of about 2-8 carbon atoms. Illustrative non-limiting examplesof such α-olefins are ethylene, propylene, 1-butene, 1-pentene,4-methyl-1-pentene, 1-hexene, 1-octene, and 1-dodecene and the like.Polyene comonomers suitable for the copolymerisation with propylene orbutene to form propylene or butane copolymers suitable for the presentinvention have, in the main, about 3 to 20 carbon atoms, preferably inthe range of about 4 to about 20 carbon atoms, most preferably in therange of about 4 to about 15 carbon atoms. In one embodiment the polyeneis a diene that has in the range of about 3 to about 20 carbon atoms,and may be a straight chained, branched chained or cyclic, hydrocarbondiene. Preferably the diene is a non-conjugated diene. Non-limitingexamples of propylene or butene α-olefin plastomers suitable for thepresent invention include propylene or butene/butene-1, propylene orbutene/hexene-1, propylene or butene/octene-1 and propylene orbutane/ethylene copolymers. Non-limiting examples of terpolymerpropylene or butene plastomers suitable for the present inventioninclude ethylene/propylene or butene/1,4 hexadiene and propylene orbutene/octene-1/1,4-hexadiene. Copolymers of propylene or butene withother α-olefins having 2 to 8 carbon atoms that are particularly usefulfor the present invention are copolymers comprising propylene or butaneand ethylene as indispensable components (monomer units) as well ascopolymers of propylene or butene with ethylene and at least oneα-olefin having 4 to 8 carbon atoms usable herein include, for example,1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene,and 1-octene. Further, the copolymer way contain as a comonomer 0.5 to10% by weight of a nonconjugated diene, such as 1,4-hexadiene,5-methyl-1,5-hexadiene, 1,4-octadiene, cyclohexadiene, cyclooctadiene,dicyclopentadiene, 5-ethylidene-2-norbornene, 5-butylidene-2-norbornene,or 2-isopropenyl-5-norbornene. Preferably these copolymers are preparedusing metallocene or similar catalysts. The percentages of ethyleneand/or other α-olefins copolymerised with propylene or butene to formpolymers suitable for the present invention can be varied widely,depending on the desired properties of the mouldings made from blends ofthese materials. In general, the higher the percentage of ethyleneand/or α-olefin copolymer polymerised with the propylene or butene, thelower the flex modulus of the resultant polymer and so the more flexiblethe mouldings made from them will be in which said polymers constitutethe polymer of the blend.

U.S. Pat. No. 6,355,736, which is hereby incorporated by reference,describes a propylene block copolymer composition comprising (A) apropylene-olefin random copolymer with a propylene content of 99.4 to99.9 mol % and (B) a propylene-α-olefin random copolymer with apropylene content of 35 to 60 mot %. It further describes propyleneblock copolymer compositions wherein the content of thepropylene-α-olefin random copolymer (B) is from 22 to 40% by weightbased on the weight of the propylene block copolymer composition. Suchpropylene block copolymers are suited for use as the polymer componentand/or the high melt flow compatible polymer in the present invention.

U.S. Pat. No. 6,458,901, which is hereby incorporated by reference,describes propylene copolymers suitable for use as the polymer componentand/or the high melt flow compatible polymer suitable for use in thepresent invention. The propylene copolymers described comprisepropylene, at least one olefin selected from the group consisting ofolefins having 2 to 20 carbon atoms except propylene, and a cyclicolefin, and are characterized in that the total number of carbon atomsof the monomers except the cyclic olefin is at least 7. Theincorporation of cyclic olefins into polymers consisting of propylene,at least one olefin selected from the group consisting of olefins having2 to 20 carbon atoms except propylene results in the improvement of theheat resistance of the resultant polymer. The propylene copolymerpreferably contains 0.01 to 20% by mole, more preferably 0-05 to 15% bymole, particularly preferably 0.1 to 10% by mole, most preferably 0.15to 5% by mole, of the cyclic olefin. When the propylene copolymer of thepresent invention comprises ethylene (the olefin having two carbonatoms), the content of ethylene is preferably 80% by mole or less, morepreferably 70% by mole or less, particularly preferably 60% by mole orless, most preferably 50% by mole or less, from the viewpoint of theimprovement of flexibility of the thermoplastic resin composition.

The short chain branch distribution index (SCBDI) is defined as theweight percent of molecules having a comonomer content within 15% of themedian total molar comonomer content. The SCBDI of the propylenepolymers suitable for the present invention is preferably greater thanabout 30%, and especially greater than about 30%, with figures of 70% ormore being achievable.

Unless otherwise stated, when a copolymer is described as having acertain percentage of a particular monomer in its composition, forexample a propylene/ethylene copolymer with 5% ethylene, it means thatthe copolymer consists of 5% by weight of ethylene-derived units out ofthe sum of the weights of propylene and ethylene-derived units, in thisparticular case this being 100%.

Unless otherwise stated, MWD (molecular weight distribution) ma theratio of the weight average molecular weight to the number averagemolecular weight, i.e. Mw/Mn.

Unless otherwise stated, ‘crystallizable’ (eg. as used in‘propylene/ethylene copolymer with isotactic propylene crystallisablesequences’) means that a particular polymer or blend has generallycrystallisable sequences of a particular type (eg. isotactic propylene)which may be identified by the heat of fusion characteristic of theparticular crystallisable sequences as highlighted in DSC analysis.

Examples of blends utilising the benefits of the addition of a high meltflow compatible polymer into the polymer are clearly illustrated by thefollowing examples:

Example 1

A 25:37.5:37.5 blend of SC973:Engage 8401:WSM 168 was injection mouldedinto tubes and the ESCR tested. SC973 is the compatible polymer in thisformulation and is a 100 MFI PP obtained from Basell. This formulationhad a ±30% ESCR failure rate after 360 hours.

Example 2

A 25:37.5:37.5 blend of Atofina 3960:Engage 8401:WSM 168 was injectionmoulded into tubes and the ESCR tested. Atofina 3960 is the compatiblepolymer in this formulation, and is a 350 MFI PP obtained from Atofina.This formulation showed a 0% ESCR failure rate after 360 hrs as well assignificantly improved clarity relative to the comparative formula.

The only difference between the formulations of Examples 1 and 2 is thesubstitution of the high melt flow compatible polymer approximatelychemical equivalent of the compatible polymer for the compatiblepolymer, with the key difference between them being the much higher MFIof the high melt flow compatible polymer relative to the compatiblepolymer. The significant improvement in ESCR performance is due to themuch higher MFI (i.e. much lower MW) of the high melt flow compatiblepolymer relative to the compatible polymer.

Examples of blends according to the second aspect of the invention willnow be described. It will be understood that the percentages of thevarious types of blend components illustrated in these example may bevaried depending on the desired properties of the mouldings producedtherefrom, and that the range of percentages of the types of blendcomponents that will produce acceptable mouldings may be determined byexperimentation.

Example 3

-   70% propylene/butene copolymer with a butene content of 15%, an of    50 and a MWD of <4 and made by a metallocene/single site catalyst.-   30% Exact 4038, a 125 MFI 0.885 density ethylene/butene copolymer    from ExxonMobil.

This example illustrates the incorporation of a high MFI mPE compatiblepolymer into a propylene/α-olefin copolymer, and which is suitable forthe manufacture of tin-walled flexible articles.

Example 4

-   70% propylene/octene copolymer with an octene content of 20%, an MFI    of 30 and a MWD of <4 and made by a metallocene/single site catalyst-   30% of Fina 3960, a 350 MFI PP homopolymer from Atofina.

This example illustrates the incorporation of a high MFI PP compatiblepolymer into a propylene/octene α-olefin copolymer, and which issuitable for the manufacture of thin-walled flexible articles.

Example 5

-   70% propylene/ethylene substantially linear copolymer with an    ethylene content of 25%, an MFI of 50 and a MWD of <4 and made by    metallocene/single site catalysts.-   30% of Fina 3960, a 350 MFI PP homopolymer from Atofina.

This example illustrates the incorporation of a high MFI PP compatiblepolymer into a substantially linear propylene/ethylene α-olefincopolymer, and which is suitable for the manufacture of thin-walledflexible articles.

Example 6

-   80% propylene/butene copolymer plastomer with an butene content of    30%, an MFI of 70 and a MWD of <4 and made by a metallocene/single    site catalyst.-   10% of a 50 MFI isotactic or syndiotactic PP homopolymer made using    a metallocene/single site catalyst-   10% of Fina 3960, a 350 MFI PP homopolymer from Atofina.

This example illustrates the incorporation of a high MFI PP and a lowMFI PP compatible polymer into a propylene/butene α-olefin copolymerplastomer, and which is suitable for the manufacture of thin-walledflexible articles.

Example 7

-   90% propylene/butene copolymer with an butene content of 30%, an MFI    of 70 and a MWD of <4 and made by a metallocene/single site    catalyst.-   10% of a 500 MFI polyethylene or ethylene α-olefin copolymer made    with a metallocene catalyst.

This example illustrates the incorporation of a high MFI polyethylene orethylene α-olefin copolymer as the compatible polymer in combinationwith a propylene/butene α-olefin copolymer. The α-olefin percentage itthe copolymer may be varied from 0.5% to 49% depending on requirementsof the end use.

Example 8

-   90% propylene/butene copolymer with a butene content of 30%, an MFI    of 150 an a MWD of >4 and made by a metallocene/single site    catalyst.-   10% of a 500 MFI polyethylene, preferably made by a    metallocene/single site catalyst.

This example illustrates the incorporation of a high MFI polyethylene asthe compatible polymer in combination with a high MFI polypropylenecompatible polymer.

Example 9

-   40% propylene/ethylene copolymer with a density of 0.86 and reduced    isotacticity, and MFI of 14 such as Vistamaxx 1120 (ExxonMobil)-   60% of Fina 3960, a 350 MFI PP homopolymer from Atofina.

This example illustrates the incorporation of a high crystallinity, highMFI PP polymer into a propylene/ethylene α-olefin copolymer with alteredtacticity and reduced isotacticity, and which is suitable for themanufacture of thin-walled flexible articles.

Example 10

-   30% propylene/ethylene copolymer with an MFI of 14, a density of    0.86 and altered tacticity such as Vistamaxx 1120.-   30% of a 50 MFI isotactic or syndiotactic PP random copolymer and-   40% of Fina 3960, a 350 MFI PP homopolymer from Atofina.

This example illustrates the incorporation of a high PP and a low MFIpropylene/ethylene copolymer with statistic distribution of stereoscopicerrors together with a PP random copolymer. This blend is suitable forthe manufacture of thin-walled flexible articles and which has improvedclarity and a lower tendency to stress whiten due to the incorporationof the random copolymer in place of some of the PP homopolymer.

Example 11

-   35% propylene/ethylene copolymer with stereoscopic errors having and    MFI of 300, density of 0.86 and a flex modulus (1% secant) of    approximately 13 MPa-   65% 100 MFI random PP copolymer

This example illustrates the incorporation of a very high MFIpropylene/ethylene copolymer with stereoscopic errors in a readilyavailable grade of prior art random PP copolymer to produce a relativelyhigh MFI blend that is suitable for the manufacture of thin walledflexible articles.

Example 12

-   35% propylene/ethylene copolymer with stereoscopic errors having an    MFI of 300, density of 0.86 and a flex modulus (1% secant) of    approximately 13 MPa-   40% 100 MFI random PP copolymer-   25% 100 MFI PP copolymer such as Basell's SC973

This example illustrates the incorporation of a very high MFIpropylene/ethylene copolymer with stereoscopic errors in a readilyavailable grade of prior art random PP copolymer and a readily availablegrade of prior art PP copolymer to produce a relatively high MFI blendthat is suitable for the manufacturer of thin walled flexible articles.

Further to the above description, developments in the production ofhighly-branched polyolefins have enabled the production of star, comb,nanogel and other similar polymers. These polymers feature a pluralityof polyolefin arms linked to a polymeric backbone to provide a highlybranched structure in which the properties of the highly branchedstructure can be conveniently tailored to the application for which thepolymer is used. The choice of specific reactive polymeric backboneand/or its manner of preparation controls the branched structure as tocomb, star, nanogel or structural combinations thereof. That allows forthe preparation of polymers having relatively low viscosities comparedto their linear counterparts at the same absolute molecular weight.These polymer types and blends made therefrom may be particularlysuitable for the production of injection moulded flexible thin walledmouldings. The rheological behaviour of these polymers with controlledbranching shows surprising and useful features. These polymersfrequently have a zero-shear viscosity that is larger than a linearpolymer of the same molecular weight. They show a rapid drop inviscosity with shear rate (large degree of shear thinning) and a plateaumodulus that is at least two times lower than that of prior art linearand branched polymers. This latter characteristic is especiallysurprising, since ethylene polymers of various types exhibit essentiallythe same plateau modulus. This was thought to be intrinsic to themonomer type and not dependent on polymer architecture. The lowerplateau modulus means that the comb and similar polymers are much lessentangled than the linears, thus giving them such low viscosity fortheir molecular weight. The utility of these properties of thesepolymers is that hey have a very low viscosity for their molecularweights under melt processing conditions and so will process much moreeasily than the prior art polymers. Even when added in relatively smallquantities to conventional blends suitable for injection mouldedflexible thin walled mouldings, they can significantly improve blendprocessability. U.S. Pat. No. 6,355,757 and U.S. Pat. No. 6,084,030amongst other patents describe the production of polymers such as aredescribed above.

The copolymers of the above and similar inventions have utility inblends suitable for the production of injection moulded flexible thinwalled mouldings, those blends comprising the branched copolymer of theinventions at a very wide range (eg. 0.1-99.9% weight percent), but mostoften between 1-5%. Depending on the properties of a specifichighly-branched polymer of the above inventions and the desiredproperties of a particular formulation, said polymer may be used as acomponent of the at least one polymer or at least one compatible polymerpart of the composition of the present invention. Depending on theirproperties they may also be regarded as additives rather than componentsof the polymer portion of the present invention.

Recent catalyst and process developments have enabled the production ofa variety of polypropylene homo and copolymers possessing propertiesthat make them particularly useful for the production of injectionmoulded flexible thin walled articles. Amongst these useful polymers areelastomeric PP homo and copolymers polymers produced by altering thetacticity of the polymer by various means as well as the ability toproduce low flex modulus PP α-olefin copolymers with relatively lowpercentages of α-olefin copolymers.

As examples of one of these recent developments are linear or branchedisotactic polymers, particularly polypropylene and polybutenehomopolymers or random copolymers which have a structure in which theirtacticity varies within the range of between 25 and 60% of [mmmm] pentadconcentration. This variation in tacticity is due to the statisticdistribution of stereoscopic errors in the polymer chains. Such polymersare described in, amongst others, WO 01/27169 (P&G), WO 99/52955(Rieger) and WO 99/52950 (Rieger). Similarly, propylene/ethylenecopolymers of the types described in U.S. Pat. No. 6,525,157(ExxonMobil) are suitable for use in injection moulded flexible thinwalled mouldings. It is worth noting that propylene α-olefins in whichthe number of Cs in the α-olefin is >4 have particular utility forpackaging requiring improved cold creep resistance relative to propyleneα-olefins in which the number of Cs in the α-olefin is ≦4.

When the at least one polymer of a blend is a linear, substantiallylinear or branched polymer in which propylene or butene constitutes over50% of the polymer, the MFI of the at least one polymer homo or α-olefincopolymer may be higher than is generally acceptable when ethyleneα-olefins constitute the at least one polymer due to propylene andbutene homo or α-olefins generally possessing better inherent ESCRproperties at the same MFI compared to most ethylene α-olefins. Thussome propylene and butane homo or α-olefin copolymers, particularlythose prepared by metallocene or similar catalysts, may have MFIs up toand greater than 50 and still produce acceptable injection mouldedflexible thin wailed mouldings with good ESCR when used as the at leastone polymer. The optimum MFI for a particular propylene or butene homoor α-olefin copolymer at least one polymer can be determined byexperimentation, but will preferably be >30, more preferably >50 and,depending on the characteristics of the particular polypropylene orpolybutene homo or α-olefin copolymer, may be even more preferably >100and often >150. α-olefins suitable for copolymerisation with propyleneor butene to produce propylene or butene α-olefins suitable forinjection moulded flexible thin walled mouldings include α-olefins inthe range of about 2 to about 20 carbon atoms, preferably in the rangeof about 2-16 carbons, most preferably in the range of about 2-8 carbonatoms. Further, the copolymer may contain as a comonomer 0.5 to 10% byweight of a nonconjugated diene, such as 1,4-hexadiene,5-methyl-1,5-hexadiene, 1,4-octadiene, cyclohexadiene, cyclooctadiene,dicyclopetadiene, 5-ethylidene-2-norbornene, 5-butylidene-2-norbornene,or 2-isopropenyl-5-norbornene. Preferably these copolymers are preparedusing metallocene or similar catalysts. The percentages of ethylene andor other α-olefins copolymerised with propylene or butene to formpolymers suitable for injection moulded flexible thin walled mouldingscan be varied widely, depending on the desired properties of themouldings made from blends of these materials. In general, the higherthe percentage of ethylene and/or other α-olefin copolymer polymerisedwith the propylene or butene, the lower the flex modulus of theresultant polymer and so the more flexible the mouldings made from themwill be in which said polymers constitute the at least one polymer ofthe blend.

Blends designed for recoverability and which contain a dispersed phaseor co-continuous phase of a greater crystallinity and a continuous orco-continuous phase of lesser crystallinity such as are described beloware suitable for the production of injection moulded flexible thinwalled mouldings. The sizes of the individual domains of the dispersedphase in these blends are preferably very small. The components of theblend are also compatible to the extent that no compatibiliser needs tobe added to attain and retain this fine morphology. One of thecomponents is a polymer comprising predominately stereospecificpolypropylene, preferably isotactic polypropylene. This is the componentwith greater crystallinity (an XPP). A second component is a copolymerof propylene and at least one C₂, C₄-C₂₀ α-olefin preferably ethylene.This is the component with lesser crystallinity (an SXPP). In thecopolymer the propylene is preferably polymerised substantiallystereospecifically. Preferably the copolymer has a substantially uniformcomposition distribution, preferably as a result of polymerisation witha metallocene catalyst. Most preferably, said SXPP is an ethylenepropylene copolymer, e.g. ethylene propylene semicrystalline elastomer.

It has been found that blending an at-least-one XPP and an at-least-oneSXPP results in advantageous processing characterstics while stillproviding a composition having decreased flexural modulus and increasedtensile strength, elongation, recovery and overall toughness. A thirdpolymeric component which is another crystallizable propylene α-olefincopolymer (an SPX2) has a crystallinity between those of the XP andSXPP. One type of PP blend suitable for injection moulded flexible thinwalled mouldings comprises a crystalline isotactic or syndiotacticpolypropylene (XPP) with a semi-crystalline α-olefin PP copolymer (SXPP)of the same tacticity as the XPP, preferably an ethylene propylenecopolymer containing 4 wt. % to 35 wt. % α-olefin, preferably ethylene,and optionally a second propylene α-olefin copolymer with acrystallinity intermediate between the XPP and SXPP and preferably withsimilar tacticity. These blends have heterophase morphology. It isbelieved that this matching of stereoregularity increases thecompatibility of the components and results in improved adhesion at theinterface of the domains of the polymers of different crystallinities.In the polymer blend composition. Narrow intermolecular andintermolecular compositional distribution in the copolymer is preferred,but not essential. These and similar blends may be particularly suitablefor the manufacture of flexible injection moulded flexible thin walledmouldings and other containers that are subjected to heating by suchmethods as heat-filling with the product the container is required tocontain and/or heat treating the filled container by methods such asresorting. Blend composition can vary widely depending on theapplication and may comprise 1% to 95% by weight of XPP and a SXPP withgreater than 65 percent by weight propylene and preferably greater than80% by weight propylene.

Polypropylene-based at least one polymer compositions that have low flexmodulus have particular utility for injection moulded flexible thinwalled mouldings. The following are illustrations of some broadformulations that are capable of providing suitable low-flex-modulus PPcompositions.

Formulation Type 1:

-   1. 8-25% crystalline PP or PP copolymer, most preferably 12-18%. If    it is a copolymer, it should have at least 85% by weight of PP,    preferably more than 90%.-   2. 75%-92%, most preferably 82-88%, of two elastomeric polymers.    Polymer a) and Polymer b): Polymer a) having 15-32% α-olefin,    preferably 25-30%, optionally including 0.5-5% diene and Polymer b)    having 32-45% α-olefin, preferably 35-40%, optionally including    0.5-5% diene. The weight ratio of polymer a) to polymer b) is 1:5 to    5:1.

The above composition may be prepared by sequential polymerisation orblending. The preferred α-olefin is ethylene. Depending on propertiesneeded, the above compositions may be used in combination with EPR(ethylene/propylene copolymers), ethylene/propylene/diene terpolymers(EPDM), ethylene/C₄-C₁₂ α-olefins (eg. ethylene/octane such as Engage).Such elastomeric polymers may be present in 5%-80% weight ofcomposition.

Formula Type 2:

-   1. 10-60% of a crystalline propylene homo or co polymer-   2. 10-40% propylene/ethylene copolymer insoluble in xylene (i.e. low    ethylene copolymer content) and-   3. 30-60% ethylene/propylene copolymer soluble in xylene at room    temp (i.e. high ethylene copolymer content)

The above composition may be prepared by sequential polymerisation orblending.

Formula Type 3:

-   1. 70-98% of a crystalline PP homo or copolymer-   2. 2-30% somewhat xylene insoluble propylene/ethylene copolymer    (i.e. relatively low ethylene copolymer)

This blend has a relatively high flex mod, due to the relatively high %crystalline copolymer and relatively low α-olefin PP copolymer, and maybe prepared by sequential polymerisation or blending.

Other types of formulations include simple blending of a variety ofdifferent types of PP at least one polymers such as have been mentionedabove, preferably PP homo polymers of different tacticities and PPα-olefin copolymers of various tacticities and degrees of α-olefincontent together with at least one compatible polymers of various types,particularly mPEs and PP homopolymers of different tacticities and PPα-olefin copolymers of various tacticities and degrees of α-olefincontent having a lower flex modulus than the PP at least one polymerused in the particular blend.

In addition to its use in PP blends, blends of HD/MD/LDPE with PEcopolymers that can act as ‘tie molecules’, eg. low density mPE, canalso be improved using the techniques of sperulite boundarystrengthening. This enable the tie molecules to be concentrated at thecrystal boundary, which effectively increases the number of tiemolecules at the crystal interface, which in turn leads to increasedblend ESCR.

It will be understood by those skilled in the art that the percentagesof the various types of blend components illustrated in the aboveexamples may be varied depending on the desired properties of themoulding, and that the range of percentages of the types of blendcomponents that will produce acceptable mouldings may be determined byexperimentation.

The claims defining the invention are as follows:
 1. A process for themanufacture of flexible thin-walled articles including: injectionmoulding a blend of (a) at least one polymer and (b) at least one highmelt flow compatible polymer having an MFI of greater than
 100. 2. Aprocess according to claim 1, wherein the high melt flow compatiblepolymer has an MFI of greater than
 200. 3. A process according to claim2, wherein the high melt flow compatible polymer has an MFI of greaterthan
 300. 4. A process according to claim 1, wherein at least one of (a)and (b) includes a polymer formed using a metallocene or similarcatalyst system.
 5. A process according to claim 4, wherein bothcomponents (a) and (b) include a propylene and/or ethylene polymer orcopolymer.
 6. A process according to claim 1, wherein component (a) ispresent in an amount of from about 40 to about 99.9 weight percent ofthe blend based on the total weight of (a) and (b) and forms thecontinuous or co-continuous phase of the blend.
 7. A process accordingto claim 1, wherein the blend further includes (c) nanoparticlesdispersed therein.
 8. A process according to claim 1, wherein theextractables content for the compositions of the invention and mouldingstherefrom is less than or equal to 2.0 wt %.
 9. A process according toclaim 1, wherein the at least one polymer (a) is a plastomer,substantially linear or branched polymer in which polypropyleneconstitutes over 50% of the polymer and which has an MFI of greater than100.
 10. A process according to claim 1, wherein (a) and/or (b) is apolypropylene homo- or co-polymer in which the tacticity varies withinthe range of between 25 and 60% [mmmm] pentad concentration.
 11. Theprocess according to claim 1, wherein (a) is a propylene polymer with5-25% by weight ethylene-derived units.
 12. The process according toclaim 1, wherein the flexible thin-walled article is a tube.